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Carahart's notch

Carahart's notch:
Is classically found in bone conduction audiograms of patients with
otosclerosis. This is actually a dip centered around 2000 Hz.

Figure showing carahart's notch

Some authors consider carhart's notch to be an artifact. This notch is closely related to the carhart's effect.Carhart's effect:
was initially described following successful stapes surgery. There was
an over closure of air bone gap following successful surgery.
Classically this effect lead to an improvement in hearing levels
particularly at 2 KHz frequency levels.

How carhart's effect is created?When skull is vibrated by bone conduction, sound is transferred to cochlea via three routes. i.e.1. By direct vibration of skull2. By vibration of ossicular chain which is suspended within the skull3. By transmission via external auditory canal (normal route)In
conductive hearing loss routes 2 and 3 are affected, but can be
regained following successful stapes surgery. Hence bone conduction
thresholds improve around 2 KHz frequency range.